1. Field of the Invention
The present invention relates generally to shieldable safety needle assemblies and, more particularly, to needle assemblies having a housing, a needle cannula, and a shield restrainably engaged with a portion of the housing.
2. Description of Related Art
Typical needle assemblies include a needle cannula having a proximal end, a pointed distal end with a puncture tip, and a lumen extending therebetween. A thermoplastic hub is often mounted securely to the needle cannula at a location spaced apart from the distal end. The hub is typically provided with external threads or other surface configurations for mounting the needle cannula to another structure. Some needle assemblies are used for drawing a specimen, such as a sample of blood or other bodily fluid, from a patient.
A needle assembly that is used to draw a sample of blood or other bodily fluid is typically used in association with a housing. Needle cannulae used in association with these assemblies typically have pointed proximal and distal ends, and the needle hub is mounted to a location between the opposed ends of the needle cannula. The housing typically includes a substantially tubular sidewall with a widely opened proximal end, and a partly closed distal end. The hub of the prior art needle assembly can be engaged with the partly closed distal end of the needle holder. Thus, the pointed proximal end of the needle cannula projects into the needle holder for engagement with an evacuated tube, while the pointed distal end of the needle cannula projects distally beyond the needle holder for puncturing the patient's skin.
The needle assembly is often used with a specimen collection tube for drawing a sample of blood or other bodily fluid from a patient. The specimen collection tube typically includes a closed end, an open end, and a sidewall extending therebetween. The tube is typically evacuated, and the open end is sealed by a septum that retains the vacuum within the tube. The evacuated tube is dimensioned to be slid into the open proximal end of the needle holder. Sufficient sliding of the evacuated tube into the needle holder causes the proximal point of the needle cannula to pierce the septum of the evacuated tube. Thus, the needle cannula can be placed in communication with the interior of the evacuated tube.
The combined needle assembly and evacuated tube is employed by initially urging the pointed distal end of the needle cannula into a blood vessel of a patient. Once the targeted blood vessel has been accessed, the evacuated tube is urged into the needle holder such that the proximal point of the needle cannula pierces the septum of the tube. Low pressure conditions within the evacuated tube, as well as the patient's own vasculature pressure, generate a flow of blood from the patient through the needle cannula and into the evacuated tube. The evacuated tube may be removed from the needle holder after a sufficient quantity of blood has been collected. One or more additional evacuated tubes may similarly be urged into the open end of the needle holder for drawing one or more additional samples of blood to be analyzed. The needle cannula is then withdrawn from the patient after a sufficient volume of blood has been collected for the required analytical procedure. In order to reduce the risk of an accidental needle stick, or contact that could transmit pathogens from the patient to the medical practitioner, the needle cannula must be properly shielded after contact with the patient.
Many types of devices are available for shielding a used needle cannula. Example shielding devices include those disclosed in U.S. Pat. Nos. 5,348,544; 5,242,417; 6,592,556; 6,635,032; and 7,001,363, the entire disclosures of which are herein incorporated by reference. Most shielded needle assemblies are effective at performing their primary function, i.e., shielding a used needle cannula. However, many medical practitioners consider the available shieldable needle assemblies cumbersome. Additionally, in some cases, practitioners may be rushing and forget to operate the safety shield. Other situations arise where the patient moves suddenly or unexpectedly. Thus, the needle cannula may inadvertently be pulled out of the vein and exposed with no time for the phlebotomist to initiate safety shielding.
Another problem with many prior art blood collection devices relates to the time required to assure venous entry. In particular, blood will begin to flow through the cannula upon entry of the intravenous or distal end of the cannula into the vein. However, air present in the cannula, and in the multiple sample sleeve that covers the non-patient end of the cannula, will resist the flow of blood into and through the cannula. In response, the medical practitioner will typically urge an evacuated tube into the needle holder once the practitioner is reasonably sure that the vein has been entered. The rubber stopper at the end of the evacuated tube will deform the multiple sample sleeve over the non-patient end of the cannula and will permit the non-patient end of the cannula to enter the evacuated tube. The pressure differential between the evacuated tube and the cannula will cause the blood to flow into the evacuated tube. In conventional needle assemblies, this often provides the first visual assurance that the vein has been accessed properly.
However, there are many instances in which a medical practitioner will properly access a vein with the distal end of the needle cannula, but will mistakenly believe that the vein has not been entered. Hence, the practitioner will make a second attempt to access the vein. This adds to the discomfort for the patient, extends the time required to carry out a blood collection procedure, and increases the risk for accidental contact between the medical practitioner and a cannula that has been exposed to the patient's blood. Additionally, in some instances a passive shielding mechanism will be activated when the cannula is withdrawn from the patient, thereby making the needle cannula unusable and requiring the medical practitioner to obtain a new needle assembly.